1. Field of the Disclosure
The present disclosure relates to an image forming apparatus, such as a printer, a multifunction peripheral, a copying machine, and a facsimile machine, including registration rollers for sending out a sheet after bending the sheet.
2. Description of Related Art
In an image forming apparatus, a sheet is transported and an image is formed on the sheet that is being transported. Further, there is an image forming apparatus, in which a sheet size is detected using a sensor for detecting the transported sheet. Such an image forming apparatus confirms whether or not the detected sheet size is different from a sheet size set by a user. For example, when the detected sheet size is different from the sheet size set by the user, the image forming apparatus detects that an error or a jam has occurred. The following image forming apparatus is known as an example.
There is known such a copying apparatus having at least one of a duplex copying function, a mutilayer copying function, and a reverse delivery function, and including detection means for detecting a sheet size during transportation of the sheet, determination means for determining whether or not the sheet size detected by the detection means is the same as a preset sheet size when any one of the duplex copying function, the mutilayer copying function, and the reverse delivery function is selected, control means for performing, when it is determined that the sheet size detected by the detection means is not the same as the preset sheet size, simplex copying on the sheet without executing the selected any one of the functions, and delivering the sheet outside the apparatus, and notification means for notifying, when it is determined that the sheet size detected by the detection means is not the same as the preset sheet size, that the sheet size detected by the detection means is not the same as the preset sheet size. With this configuration, it may be possible to prevent a jam caused by the transportation of the sheet having a size different from the set sheet size.
The image forming apparatus may include a registration roller pair (registration rollers) for temporarily stopping the sheet. In this case, the registration roller pair is provided on an upstream side of an image forming unit, which forms an image on the sheet, in a sheet transportation direction. The registration roller pair is used for correcting skew feed of the sheet. Specifically, a leading edge of the sheet is brought into abutment against the registration roller pair that is held in a stopped state. The sheet transportation is continued on a trailing edge side of the sheet, and accordingly the sheet is bent. Due to elasticity of the bent sheet, the leading edge of the sheet is aligned with a nip of the registration roller pair. Accordingly, the skew feed of the sheet is corrected.
Further, as in the case of the above-mentioned copying apparatus, the sheet size detection may be performed using a sensor for detecting the sheet, which is provided in the vicinity of the registration roller pair. For example, the sheet size detection may be performed based on a time period from the time when the registration roller pair is driven (rotated) to the time when the sensor detects passage of the sheet.
However, due to a slip of the sheet or the like, fluctuation occurs in the time period from the time when the registration roller pair is driven (rotated) to the time when the sensor detects the passage of the sheet. This fluctuation in time period detected by the sensor may be caused by fluctuation in bending amount of the sheet (degree of sheet bending) at the registration roller pair.
Conventionally, the sheet is bent at the registration roller pair by stopping the registration roller pair and also continuing the transportation on the trailing edge side of the sheet by rollers (for convenience, referred to as “intermediate rollers”) for performing transportation one stage upstream of the registration roller pair. After the sheet is bent, in order to prevent excessive bending of the sheet, conventionally, the intermediate rollers are temporarily stopped until the registration roller pair rotates. After the intermediate rollers are stopped, the registration roller pair and the intermediate rollers rotate to send out the sheet toward the image forming unit.
In this manner, conventionally, the drive of the intermediate rollers is turned ON and OFF when the sheet is bent. However, fluctuation occurs in response speed of the intermediate rollers. For example, there occur an individual difference in response speed of a drive ON/OFF clutch, and decrease in response speed caused by deterioration over time. Therefore, the bending amount of the sheet is not easily kept constant. In particular, in recent years, there has been a demand for higher image formation speed, and therefore increase in rotation speed of the intermediate rollers (sheet transportation speed) has been promoted. As a result, the fluctuation in ON/OFF of the drive of the intermediate rollers greatly affects the fluctuation (error) in bending amount of the sheet. The fluctuation in bending amount of the sheet increases, and accordingly the fluctuation in time period detected by the sensor increases for the same sheet size. As a result, there arises a problem of difficulty in accurate sheet size detection. The sheet size may be detected erroneously as in a case where an A4 sheet is detected as a letter size sheet.
Further, conventionally, the sheet size detection may be performed by measuring the time period from the time when the registration roller pair is driven (rotated) to the time when the sensor detects the passage of the sheet. The drive of the registration roller pair is also turned ON and OFF, but an individual difference in response speed of a drive ON/OFF clutch of the registration roller pair, and decrease in response speed caused by deterioration over time may also be factors inhibiting the accurate sheet size detection.
Note that, as described above, the above-mentioned copying apparatus performs the sheet size detection based on the time period from the time when the registration roller pair is rotated to the time when the sensor detects the passage of the sheet. However, it is necessary to take some measures for avoiding the inaccurate sheet size detection.